Phase-change materials (PCM) are capable of transforming from a crystalline phase to an amorphous phase. These two solid phases exhibit differences in electrical properties, and semiconductor devices can advantageously exploit these differences. Given the ever-increasing reliance on radio frequency (RF) commnunication, there is particular need for RF switching devices to exploit phase-change materials. However, the capability of phase-change materials for phase transformation depends heavily on how they are exposed to thermal energy and how they are allowed to release thermal energy. For example, in order to transform into an amorphous phase, phase-change materials may need to achieve temperatures of approximately seven hundred degrees Celsius (700° C.) or more, and may need to cool down within hundreds of nanoseconds.
Additionally, when transforming from a crystalline phase to an amorphous phase, PCM exhibits volume expansion which introduces stresses that cause defects in the PCM, contacts, and other structures in PCM RF switches. These defects reduce reliability and can cause failure of PCM RF switches. Over numerous cycles, PCM volume expansion (when transforming from a crystalline phase to an amorphous phase) and contraction (when transforming from an amorphous phase to a crystalline phase) can also exacerbate otherwise minor defects. Accordingly, accommodating PCM in PCM RF switches can present significant manufacturing challenges. Specialty manufacturing is often impractical, and large scale manufacturing generally trades practicality for the ability to control device characteristics.
Thus, there is a need in the art for PCM RF switches having increased reliability against defects associated with phase transformation volume expansion and contraction.